Polyamides

ABSTRACT

Polyamide containing a compound which bears at least one hydroxy group and has chemical bonding by way of an amide group to the end of the polymer chain, process for preparing this polyamide, and also fibers, films, and moldings, comprising at least one such polyamide.

The present invention relates to a polyamide containing a compound whichbears at least one hydroxy group and has chemical bonding by way of anamide group to the end of the polymer chain.

It further relates to a process for preparing this polyamide, and tofibers, films, and moldings comprising at least one such polyamide.

Polyamides, in particular nylon-6, and nylon-6,6, are industriallysignificant polymers. They are usually prepared by reacting suitablemonomers such as caprolactam, adipic acid, or hexamethylenediamine, inthe presence of water.

Unless further measures are taken, this gives polyamides which duringdownstream steps of processing, such as injection molding, have atendency to undergo uncontrolled molecular weight increase with aresultant impairment of processing properties. In particular, anincrease in melt viscosity occurs (determined as a fall-off in the meltvolume flow rate to EN ISO 1133), and in injection molding, for example,this leads to longer cycle time.

To stabilize the polyamide with respect to this type of uncontrolledmolecular weight increase, it is usual to use chain regulators duringthe preparation of the polymer, an example being propionic acid.

These chain regulators can substantially suppress the molecular weightincrease but in order to shorten cycle times in injection molding it isdesirable to increase the melt volume flow rate of polyamides to EN ISO1133 while the relative viscosity determined to DIN 51562-1 to -4,remains the same.

It is an object of the present invention to provide a process which, ina technically simple and cost-effective manner, permits the preparationof a polyamide which when compared with polyamides chain-regulated byconventional methods has higher melt volume flow rate to EN ISO 1133while the relative viscosity determined to DIN 51562-1 to -4, remainsthe same.

We have found that this object is achieved by means of the polyamidedefined at the outset, a process for its preparation, and fibers, films,and moldings, comprising at least one such polyamide.

For the purposes of the present invention, polyamides are homopolymers,copolymers, mixtures, and grafts of synthetic long-chain polyamideswhich have repeat amide groups as a substantial constituent in the mainpolymer chain. Examples of these polyamides are nylon-6(polycaprolactam), nylon-6,6 (polyhexamethyleneadipamide), nylon-4,6(polytetramethyleneadipamide), nylon-6,10 (polyhexamethylenesebacimide),nylon-7 (polyenantholactam), nylon-11 (polyundecanolactam), nylon-12(polydodecanolactam). These polyamides are known by the generic namenylon. For the purposes of the present invention, polyamides alsoinclude those known as aramids (aromatic polyamides), such aspolymetaphenyleneisophthalimide (NOMEX R Fiber, U.S. Pat. No.3,287,324), and polyparaphenyleneterephthalamide (KEVLAR R Fiber, U.S.Pat. No. 3,671,542).

The preparation of polyamides may in principle take place by twomethods.

During the polymerization of dicarboxylic acids and diamines, orpolymerization of amino acids or derivatives of these, such asaminocarboxylic nitrites, aminocarboxamides, aminocarboxylic esters, oraminocarboxylic salts, the amino end groups and carboxy end groups ofthe starting monomers or starting oligomers react with one another toform an amide group and, for example, water. The water can then beremoved from the polymer. During the polymerization ofaminocarboxamides, the amino and amide end groups of the startingmonomers or starting oligomers react with one another to form an amidegroup and ammonia. The ammonia can then be removed from the polymer.During the polymerization of aminocarboxylic esters, the amino and esterend groups of the starting monomers or starting oligomers react with oneanother to form an amide group and an alcohol. The alcohol can then beremoved from the polymer. During the polymerization of aminocarboxylicnitrites the nitrile groups may firstly be reacted with water to giveamide groups or carboxylic acid groups, and the resultantaminocarboxamides or aminocarboxylic acids can be reacted as described.This polymerization reaction is usually termed polycondensation.

The polymerization of lactams as starting monomers or starting oligomersis usually termed polyaddition.

The polyamides can be obtained by processes known per se, for examplethose described in DE-A-14 95 198, DE-A-25 58 480, EP-A-129 196 or in:Polymerization Processes, Interscience, New York, 1977, pp. 424-467, inparticular pp. 444-446, from monomers selected from the group consistingof lactams, omega-aminocarboxylic acids, omega-aminocarbonitriles,omega-aminocarboxamides, omega-aminocarboxylic salts,omega-aminocarboxylic esters, equimolar mixtures of diamines anddicarboxylic acids, dicarboxylic acid/diamine salts, dinitriles anddiamines, or mixtures of these monomers.

Monomers which may be used are

-   in the form of monomer or oligomer, a C₂-C₂₀, preferably C₂-C₁₈,    arylaliphatic or preferably aliphatic lactam, examples being    enantholactam, undecanolactam, dodecanolactam or caprolactam,-   in the form of monomer or oligomer, C₂-C₂₀, preferably C₃-C₁₈,    aminocarboxylic acids, examples being 6-aminocaproic acid,    11-aminoundecanoic acid, and the salts of these, such as alkali    metal salts, e.g. lithium salts, sodium salts, potassium salts,-   in the form of monomer or oligomer, C₂-C₂₀, preferably C₃-C₁₈,    aminocarbonitriles, examples being 6-aminocapronitrile,    11-aminoundecanonitrile,-   in the form of monomer or oligomer, C₂-C₂₀ aminocarboxamines,    examples being 6-aminocapramide, 11-aminoundecanoamide,-   esters, preferably C₁-C₄-alkyl esters, e.g. methyl, ethyl, n-propyl,    isopropyl, n-butyl, isobutyl, sec-butyl esters, of C₂-C₂₀,    preferably C₃-C₁₈, aminocarboxylic acids, examples being    6-aminocaproates, such as methyl 6-aminocaproate,    11-aminoundecanoates, such as methyl 11-aminoundecanoate,-   in the form of monomer or oligomer, a C₂-C₂₀, preferably C₂-C₁₂,    alkyldiamine, such as tetramethylenediamine or preferably    hexamethylenediamine, with a C₂-C₂₀, preferably C₂-C₁₄, aliphatic    dicarboxylic acid or its mono- or dinitrile, examples being sebacic    acid, dodecanedioic acid, adipic acid, sebaconitrile, decanonitrile,    or adiponitrile,-   in the form of monomer or oligomer, a C₂-C₂₀, preferably C₂-C₁₂,    alkyldiamine, examples being tetramethylenediamine or preferably    hexamethylenediamine, with a C₈-C₂₀, preferably C₈-C₁₂, aromatic    dicarboxylic acid or derivatives thereof, such as chlorides,    examples being 2,6-naphthalenedicarboxylic acid, and preferably    isophthalic acid or terephthalic acid,-   in the form of monomer or oligomer, a C₂-C₂₀, preferably C₂-C₁₂,    alkyldiamine, examples being tetramethylenediamine or preferably    hexamethylenediamine, with a C₉-C₂₀, preferably C₉-C₁₈,    arylaliphatic dicarboxylic acid or derivatives thereof, such as    chlorides, examples being o-, m- or p-phenylenediacetic acid,-   in the form of monomer or oligomer, a C₆-C₂₀, preferably C₆-C₁₀,    aromatic diamine, examples being m- and p-phenylenediamine, with a    C₂-C₂₀, preferably C₂-C₁₄, aliphatic dicarboxylic acid or mono- or    dinitriles thereof, examples being sebacic acid, dodecanedioic acid,    adipic acid, sebaconitrile, decanonitrile, or adiponitrile,-   aromatic diamine in the form of monomer or oligomer, a C₆-C₂₀,    preferably C₆-C₁₀, aromatic diamine, examples being m- and    p-phenylenediamine, with a C₈-C₂₀, preferably C₈-C₁₂, aromatic    dicarboxylic acid or derivatives thereof, such as chlorides,    examples being 2,6-naphthalenedicarboxylic acid, and preferably    isophthalic acid or terephthalic acid,-   in the form of monomer or oligomer, a C₆-C₂₀, preferably C₆-C₁₀,    aromatic diamine, examples being m- and p-phenylenediamine, with a    C₉-C₂₀, preferably C₉-C₁₈, arylaliphatic dicarboxylic acid or    derivatives thereof, such as chlorides, examples being o-, m-, and    p-phenylenediacetic acid,-   arylaliphatic diamine in the form of monomer or oligomer, a C₇-C₂₀,    preferably C₈-C₁₈, arylaliphatic diamine, examples being m- and    p-xylylenediamine, with a C₂-C₂₀, preferably C₂-C₁₄, aliphatic    dicarboxylic acid or mono- or dinitriles thereof, examples being    sebacic acid, dodecanedioic acid, adipic acid, sebaconitrile,    decanonitrile, and adiponitrile,-   in the form of monomer or oligomer, a C₇-C₂₀, preferably C₈-C₁₈,    arylaliphatic diamine, examples being m- and p-xylylenediamine, with    a C₆-C₂₀, preferably C₆-C₁₀, aromatic dicarboxylic acid or    derivatives thereof, such as chlorides, examples being    2,6-naphthalenedicarboxylic acid, or preferably isophthalic acid or    terephthalic acid,-   in the form of monomer or oligomer, a C₇-C₂₀, preferably C₈-C₁₈,    arylaliphatic diamine, examples being m- and p-xylylenediamine, with    a C₉-C₂₀, preferably C₉-C₁₈, arylaliphatic dicarboxylic acid or    derivatives thereof, such as chlorides, examples being o-, m-, and    p-phenylenediacetic acid,-   and also homopolymers, copolymers, mixtures, and grafts of these    starting monomers or starting oligomers.

Particular oligomers which may be used are the dimers, trimers,tetramers, pentamers, or hexamers of the monomers mentioned, or ofmixtures of these monomers.

In one preferred embodiment, the lactam used is caprolactam, the diamineused comprises tetramethylenediamine, hexamethylenediamine, or a mixtureof these, and the dicarboxylic acid used comprises adipic acid, sebacicacid, dodecanedioic acid, terephthalic acid, isophthalic acid, or amixture of these. Caprolactam is particularly preferred as lactam, asare hexamethylenediamine as diamine and adipic acid or terephthalic acidor a mixture of these as dicarboxylic acid.

Particular preference is given here to those starting monomers orstarting oligomers which during the polymerization give the polyamidesnylon-6, nylon-6,6, nylon-4,6, nylon-6,10, nylon-6,12, nylon-7,nylon-11, nylon-12 or the aramids polymetaphenyleneisophthalamide orpolyparaphenyleneterephthamide, in particular to those which givenylon-6 or nylon-6,6.

In one preferred embodiment, use may be made of one or more chainregulators during preparation of the polyamides. Compounds which may beused advantageously as chain regulators are those which have one ormore, for example two, three, or four, and in the case of systems in theform of fibers preferably two, amino groups reactive in polyamideformation, or one or more, for example two, three, or four, and in thecase of systems in the form of fibers preferably two, carboxy groupsreactive in polyamide formation.

In the first case the result is polyamides in which the monomers andchain regulators used to prepare the polyamide have more of the aminegroups used to form the polymer chain, or of their equivalents, than ofcarboxylic acid groups used to form the polymer chain, or theirequivalents.

In the second case the result is polyamides in which the monomers andchain regulators used to prepare the polyamide have more of thecarboxylic acid groups used to form the polymer chain, or of theirequivalents, than of amine groups used to form the polymer chain, ortheir equivalents.

Chain regulators which may be used with advantage are monocarboxylicacids, examples being alkanecarboxylic acids, such as acetic acid andpropionic acid, and other examples being a benzene- ornaphthalenemonocarboxylic acid, such as benzoic acid, and dicarboxylicacids, such as C₄-C₁₀ alkanedicarboxylic acid, e.g. adipic acid, azelaicacid, sebacic acid, dodecanedioic acid, C₅-C₈ cycloalkanedicarboxylicacid, for example cyclohexane-1,4-dicarboxylic acid, or a benzene- ornaphthalenedicarboxylic acid, such as terephthalic acid, isophthalicacid, naphthalene-2,6-dicarboxylic acid, and C₂-C₂₀, preferably C₂-C₁₂,alkylamines, such as cyclohexylamine, C₆-C₂₀, preferably C₆- C₁₀,aromatic monoamines, such as aniline, or C₇-C₂₀, preferably C₈-C₁₈,arylaliphatic monoamines, such as benzylamine, and C₄-C₁₀alkanediamines, e.g. hexamethylenediamine.

The chain regulators may be unsubstituted or substituted, for examplewith aliphatic groups, preferably C₁-C₈-alkyl groups, such as methyl,ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, n-pentyl,n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, OH,═O, C₁-C₈-alkoxy, COOH,C₂-C₆-carbalkoxy, C₁-C₁₀-acyloxy, or C₁-C₈-alkylamino, or sulfonic acidor salts thereof, such as alkali metal or alkaline earth metal salts,cyano, or halogens, such as fluorine, chlorine, bromine. Examples ofsubstituted chain regulators are sulfoisophthalic acid, the alkali metalor alkaline earth metal salts thereof, such as the lithium salts, sodiumsalts, or potassium salts, sulfoisophthalic esters, for example thosewith C₁-C₁₆ alkanols, and sulfoisophthalic mono- or diamides, inparticular with monomers suitable for forming polyamides and bearing atleast one amino group, for example hexamethylenediamine or6-aminocaproic acid.

Chain regulators used with preference are sterically hindered piperidinederivatives of the formula

where

-   -   R¹ is a functional group capable of amide formation with respect        to the polymer chain of the polyamide, preferably a —(NH)R⁵        group, where R⁵is hydrogen or C₁-C₈-alkyl, or is a carboxy group        or a carboxy derivative or a —(CH₂)_(x)(NH)R⁵ group where X is        from 1 to 6 and R⁵ is hydrogen or C₁-C₈-alkyl, or is a        —(CH₂)_(y)COOH group where Y is from 1 to 6, or is an acid        derivative of —(CH₂)_(y)COOH where Y is from 1 to 6, and in        particular is an —NH₂ group,    -   R² is an alkyl group, preferably a C₁-C₄-alkyl group, such as        methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,        sec-butyl, in particular a methyl group,    -   R³ is hydrogen, C₁-C₄-alkyl, or O—R⁴, where R⁴ is hydrogen or        C₁-C₇-alkyl, and in particular R³is hydrogen.

In compounds of this type, steric hindrance usually prevents reaction ofthe tertiary, and in particular the secondary, amino groups of thepiperidine ring system.

A particularly preferred sterically hindered piperidine derivative is4-amino-2,2,6,6-tetramethylpiperidine.

A chain regulator may be used advantageously in amounts of at least0.001 mol %, preferably at least 0.01 mol %, in particular at least 0.03mol %, particularly preferably at least 0.08 mol %, based on 1 mole ofamide groups of the polyamide.

A chain regulator may advantageously be used in amounts of not more than2.0 mol %, preferably not more than 1 mol %, in particular not more than0.6 mol %, particularly preferably not more than 0.5 mol %, based on 1mole of amide groups of the polyamide.

According to the invention, the polyamide contains a compound whichbears at least one hydroxy group and has chemical bonding by way of anamide group to the end of the polymer chain.

For the purposes of the present invention, the expression compound whichbears at least one hydroxy group also means a mixture of such compoundswhich bears at least one hydroxy group.

The compound which bears at least one hydroxy group may bear one ormore, for example 2, 3, 4, 5 or 6 hydroxy groups, preferably 1, 2 or 3hydroxy groups, in particular one hydroxy group.

The compound used which bears at least one hydroxy group isadvantageously a monocarboxylic acid which bears at least one hydroxygroup.

The compound used which bears at least one hydroxy group isadvantageously a monoamine which bears at least one hydroxy group.

The compound used which bears at least one hydroxy group mayadvantageously be a compound which bears at least one terminal hydroxygroup.

If the compound which bears at least one hydroxy group is a monoaminewhich bears at least one hydroxy group, use may in particular be made ofa linear, unbranched alkanemonoamine.

If the compound which bears at least one hydroxy group is amonocarboxylic acid which bears at least one hydroxy group, use may inparticular be made of a linear, unbranched alkanemonocarboxylic acid,particularly preferably one of the formulaHO—(CH₂)_(n)—COOHwhere n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, inparticular n=5.

These monocarboxylic acids which bear at least one hydroxy group areknown per se, as is their preparation.

These monoamines which bear at least one hydroxy group are known per se,as is their preparation.

The content of the compound which bears at least one hydroxy group mayadvantageously be at least 0.001 mol %, preferably at least 0.01 mol %,in particular at least 0.03 mol %, particularly preferably at least 0.08mol %, based on 1 mole of amide groups of the polyamide.

The content of the compound which bears at least one hydroxy group mayadvantageously be not more than 2.0 mol %, preferably not more than 1mol %, in particular not more than 0.6 mol %, particularly preferablynot more than 0.5 mol %, based on 1 mole of amide groups of thepolyamide.

The polyamides of the invention can be obtained by reacting monomers,oligomers, or mixtures of these suitable for forming a polyamide to givea polyamide in the presence of a compound which bears at least onehydroxy group or a compound which under the reaction conditions forpreparing the polyamide makes available the compound which bears atleast one hydroxy group.

The compound used under the reaction conditions for preparing thepolyamide to make available the monocarboxylic acid which bears at leastone hydroxy group may be one where at least one of the hydroxy groups ismade available under the reaction conditions. The compounds may also bethose where the carboxylic acid group is made available under thereaction conditions, for example nitrites, esters, or amides. Thecompounds used under the reaction conditions for preparing the polyamideto make available the monocarboxylic acid which bears at least onehydroxy group may also be a compound where at least one of the hydroxygroups and the carboxylic acid group are made available under thereaction conditions.

The compound used under the reaction conditions for preparing thepolyamide to make available the monoamine which bears at least onehydroxy group may be a compound where at least one of the hydroxy groupsis made available under the reaction conditions. Use may also be made ofcompounds where the amine group is made available under the reactionconditions, for example amides. Other compounds which can be used underthe reaction conditions for preparing the polyamide to make availablethe monoamine which bears at least one hydroxy group are those where atleast one hydroxy group and the amine group are made available under thereaction conditions.

To prepare the polyamides of the invention, use may be made of theconventional process conditions for preparing polyamides from thecorresponding monomers, for example as described in DE-A-14 95 198,DE-A-25 58 480, EP-A-129 196, DE-A-19 709 390, DE-A-35 34 817, WO99/38908, WO 99/43734, WO 99/43732, WO 00/24808, WO 01/56984 or inPolymerization Processes, Interscience, New York, 1977, pp. 424-467, inparticular pp. 444-446.

In one preferred embodiment, the polymerization or polycondensation maybe carried out by the process of the invention in the presence of atleast one pigment. Preferred pigments are titanium dioxide, preferablyin the anatase or rutile crystalline form, or inorganic or organiccolorant compounds. The pigments are preferably added in amounts of from0 to 5 parts by weight, in particular from 0.02 to 2 parts by weight,based in each case on 100 parts by weight of polyamide. The pigments maybe introduced to the reactor with the starting materials or separatelytherefrom.

The polyamides of the invention may be used advantageously for producingfibers, films, or moldings which comprise this polyamide, or inparticular consist of this polyamide.

EXAMPLES

In the examples, solution viscosity was measured as relative solutionviscosity in 96% sulfuric acid to DIN 51562-1 to -4.

For this, 1 g of polymer was weighed out for 100 ml of solution, and thethroughflow time was measured in a Ubbelohde viscometer in comparisonwith the pure solvent.

Example 1

350 g (3.1 mol) of caprolactam, 35 g of demineralized water, and 1.6 g(8*10-3 mol) of 6-hydroxycaproic acid (purity 95%) were heated undernitrogen to an internal temperature of 270° C. in a laboratoryautoclave, and then immediately depressurized to atmospheric pressurewithin one hour, post-condensed for 60 minutes, and discharged.

The discharged polyamide was granulated, extracted with boiling water toremove caprolactam and oligomers, and then dried in a vacuum dryingcabinet. The dried extracted granules were heat-conditioned for varioustimes in the solid phase at 160° C. (5 h, 10 h, 20 h, 30 h).

Table 1 below shows the resultant relative solution viscosities aftervarious heat-conditioning times. TABLE 1 Heat conditioning time 0 h 1015 h 20 h 30 h Relative solution viscosity 2.47 2.74 2.83 2.86 3.00

Example 2

The melt behavior of four polyamide specimens from Example 1 wasstudied. For this, oscillatory shear measurements were made at 250° C.and melt viscosity measurements were carried out to ISO 11433. Thezero-shear viscosity η₀, i.e. the melt viscosity at zero shear, is afunction of the molar mass Mn for linear polyamides with Schulz-Florydistribution:η₀˜M_(n) ^(3.5)

The molar mass was determined by light scattering. FIG. 1 shows that thepolyamides prepared as in Example 1 are linear:

Example 3

Example 1 was repeated in a pressure vessel using the following mixture:400 kg (3571 mol) of caprolactam, 40 kg of demineralized water, and 1.06kg (8 mol) of 6-hydroxycaproic acid. The polyamide discharged wasextracted, dried, and heat-conditioned in the solid phase to a relativesolution viscosity of RV=2.72. An extruder was then used to compound 30%by weight of OCF 123 D 10 P glass fibers (from OCF) and 7% by weight ofLupolen KR 1270 rubber (from BASF Aktiengesellschaft) into the material(the percentages being based on the finished compounded material). Therelative solution viscosity after compounding was 2.80.

Comparative Example

Example 3 was repeated with the modification that 0.592 kg (8 mol) ofpropionic acid was used instead of 6-hydroxycaproic acid.

The relative solution viscosity after compounding was 2.79.

Melt volume rate (MVR) measurement to ISO 1133

Melt volume rate (MVR) measurements were carried out to ISO 1133 on thecompounded materials from Example 3 and from the comparative examples.The melt temperature here was 275° C. and the ram weight was 5 kg. FIG.2 shows the comparison of the melt volume rate for various residencetimes in the melt.

Flowability in two types of flow spirals (diameter 1.5 mm, 2 mm) wastested on the compounded materials from Example 3 and the comparativeexample. The temperature of the spirals was 280° C. Flow path wasmeasured in cm. Table 2 below shows the measurements: TABLE 2 Example 4Comparative example Flow spiral (1.5 mm) 26.9 cm 24.5 cm Flow spiral (2mm) 41.4 cm 38.8 cm

1. A polyamide comprising a compound which includes at least one hydroxygroup and has chemical bonding by way of an amide group to the end ofthe polymer chain, where the compound which includes at least onehydroxy group is a linear, unbranched alkanemonocarboxylic acid whichincludes at least one terminal hydroxy group.
 2. A polyamide as claimedin claim 1, where the unbranched monocarboxylic acid has the formulaHO—(CH₂)_(n)—COOH wheren=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,or
 15. 3. A polyamide as claimed in claim 1, where the unbranchedmonocarboxylic acid has the formulaHO—(CH₂)₅—COOH.
 4. A polyamide as claimed in claim 1, where the compoundwhich includes at least one hydroxy group is present in the range from0.001 to 2 mol %, based on 1 mole of amide groups of the polyamide.
 5. Aprocess for preparing a polyamide comprising providing monomers suitablefor forming a polyamide and a linear, unbranched alkanemonocarboxylicacid which includes at least one terminal hydroxy group, andpolymerizing the monomers in the presence of the unbranchedalkanemonocarobxylic acid.
 6. A process for preparing a polyamide,providing oligomers suitable for forming a polyamide and a linear,unbranched alkanemonocarboxylic acid which includes at least oneterminal hydroxy group, and polymerizing the oligomers in the presenceof the unbranched alkanemonocarobxylic acid.
 7. A fiber comprising apolyamide as claimed in claim
 1. 8. A film comprising a polyamide ofclaim
 1. 9. A molding comprising a polyamide of claim
 1. 10. A polyamideas claimed in claim 3 where the compound which includes at least onehydroxy group is present in the range from 0.001 to 2 mol %, based on 1mole of amide groups of the polyamide.
 11. A polyamide that isend-capped with an unbranched C₁-C₁₅ alkane with at least one terminalhydroxyl group.
 12. The polyamide of claim 11 where the unbranchedalkane is an attached n-pentanol.
 13. A polyamide comprising monomericor oligomeric units of an arylaliphatic lactam or aliphatic lactam,where the polyamide is end-capped with an unbranched C₁-C₁₅ alkane withat least one terminal hydroxyl group.
 14. The polyamide of claim 13where the monomeric or oligomeric units are selected from the groupconsisting of enantholactam, undecanolactam, dodecanolactam andcaprolactam.
 15. The polyamide of claim 13 where the monomeric oroligomeric units are based on caprolactam and the polyamide isend-capped by the reaction of 6-hydroxycaproic acid.
 16. The polyamideof claim 15 in combination with an inorganic or organic pigment.
 17. Apolyamide prepared by a process comprising: providing monomers oroligomers selected from an arylaliphatic or aliphatic lactam,aminocarboxylic acids or aminocarbonitriles; providing an unbranchedalkanemonocarboxylic acid having at least one terminal hydroxyl group;and polymerizing the monomer or the oligomers in the presence of theunbranched alkanemonocarboxylic acid to provide a polyamide that isend-capped with an unbranched alkane having at least one terminalhydroxyl group.
 18. The polymer of claim 17 where the monomeric oroligomeric units are based on caprolactam and the alkanemonocarboxylicacid is 6-hydroxycaproic acid.